1. Field of the Invention
The present invention relates to an organic light emitting display device and a method of fabricating the same, and more particularly, to an organic light emitting display device including a first electrode, a source electrode, and a drain electrode simultaneously formed from a silver (Ag) alloy containing samarium (Sm), terbium (Tb), gold (Au), and copper (Cu), and a method of fabricating the same.
2. Description of the Related Art
The advantages of a conventional organic light emitting display device include: low power consumption, wide viewing angle, good contrast, and fast response speed.
FIG. 1 is a cross-sectional view of a conventional top emission active matrix organic light emitting display device and a method of fabricating the same.
Referring to FIG. 1, in accordance with the conventional top emission active matrix organic light emitting display device, a buffer layer 101 is arranged on a substrate 100, and a semiconductor layer 110 including a source region 111, a drain region 112, and a channel region 113 is arranged on the buffer layer 101 in a transistor region (a).
A gate insulating layer 120 is arranged on a surface of the semiconductor layer 110, and a gate electrode 130 corresponding to the channel region 113 of the semiconductor layer 110 is arranged on the gate insulating layer 120.
An interlayer insulating layer 140 is arranged on a surface of the gate electrode 130. A source electrode 150 is electrically coupled with the source region 111 of the semiconductor layer 110 through a contact hole 141 arranged in the interlayer insulating layer 140, and a drain electrode 155 is electrically coupled with the drain region 112 of the semiconductor layer 110 through a contact hole 142 arranged in the interlayer insulating layer 140, thereby forming a thin film transistor.
For decreasing interconnection resistance, the source electrode 150 and the drain electrode 155 are formed of a low-resistance, multi-layered material, where the multi-layered material may be comprised of Al and MoW or Ti, or an Al alloy. The multi-layered material typically has a tri-layered structure of MoW/Al/MoW, MoW/Al—Nd/MoW, Ti/Al—Nd/Ti, or Ti/Al/Ti. The multi-layered material structure of MoW/Al/MoW is mostly commonly used.
MoW may have a specific resistance of 14 μΩ-cm to 15 μΩ-cm, and the source electrode 150 and the drain electrode 155 may have a line width of 6 μm.
The source electrode 150 and the drain electrode 155 may have a thickness of 4,000 Å to 6,000 Å, In this case, MoW or Ti of the source electrode 150 and the drain electrode 155 may have a thickness of 500 Å to 1,000 Å, and Al or Al—Nd may have a thickness of 3,500 Å to 5,000 Å.
At the time of forming the source electrode 150 and the drain electrode 155, a first electrode 160, which is electrically coupled with any one of the source electrode 150 and the drain electrode 155, is arranged on the same layer in an opening region.
The first electrode 160 includes a transparent conductive layer 160b and a reflective layer 160a, such as an Al or an Ag alloy among metals having high reflectivity, and patterned after deposition.
The first electrode 160 may have a thickness of 750□ to 1,300 Å. The reflective layer 160b may have a thickness of 700 Å to 1,200 Å; and the transparent conductive layer 160a, such as an Indium Tin Oxide (ITO) or an Indium Zinc Oxide (IZO), may have a thickness of 50 Å to 100 Å.
Subsequently, a pixel defining layer 180, which has an opening (b) and defines the unit pixel, is arranged on the surface of the substrate 100, including the first electrode 160 and an organic layer 180; the organic layer 180 including at least an organic emission layer arranged on the first electrode 160, exposed within the opening (b).
Subsequently, a second electrode 190 is arranged on the surface of the substrate 100 including the organic layer 180. The second electrode, which is a metal having a low work function, is formed of a thin transmissive electrode comprised of a material selected from the group consisting of Mg, Al, Ag, Ca, and an alloy thereof.
In the conventional active matrix organic light emitting display device of FIG. 1, Ag (1.61 μΩ-cm), used in the formation of the source electrode 150 and the drain electrode 155, is considered as an ideal, low-resistance interconnection material because of its low resistivity; however in manufacturing processes, the use of Ag has been limited because of Ag's weak adhesion, thermal instability, and poor chemical resistant property.
Accordingly, the source electrode 150 and the drain electrode 155 are formed from MoW, Al, or an Al alloy, and Ti instead of Ag, where MoW, Al, or the Al alloy, and Ti are typically used in a stacked structure having at least two material layers. Korean Patent Publication No. 2003-0077963 ('963) discloses an alternative method of depositing the source electrode 150 and the drain electrode 155 using a single material, which employs an Ag alloy layer using an Ag alloy target containing 0.1 to 0.5 atom % of any one of Sm, dysprosium (Dy) and Tb, and 0.1 to 1.0 atom % of Au and/or Cu. A single layer generally cannot be implemented because a step coverage or a hill-look problem causes a disconnection failure or affects a subsequent lithography process due to a change in reflectance. Accordingly, multi-layered materials, preferably having at least two layers, should be employed. However, use of multi-layered materials may cause the number of processes to increase, mass productivity to be lowered, and the electrical efficiency of the thin film transistor to be lowered because the specific resistance may be 5 μΩ-cm or higher.
The Ag alloy layer, as disclosed in '963, may provide adhesion, thermal resistance, corrosion resistance, and/or excellent patterning properties, while maintaining a low resistance property and a high reflectance property; however, when the amount of Sm, Dy, or Tb exceeds 0.5 atom %, the electrical resistance of the Ag alloy layer increases more than 4 μΩ-cm, decreasing the reflectivity of the material. The properties of the aforementioned Ag alloy layered material were determined at temperatures of 250° C. or less. Physical properties for the Ag alloy layered material have not been verified for a thin film transistor at temperatures above 250° C.
When the conventional first electrode is formed as a reflective electrode, Ag, which has the highest reflectivity among metals, has been significantly limited in its use due to adhesion, thermal resistance, and chemical resistance. To address Ag's material limitations, Al and an Al alloy were employed instead of Ag; however, use of Al or the Al alloy, caused the reflectivity and the efficiency to degrade.